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      <td><p class="toc level1"><a href="docinfo.html">Document Information</a></p>
<p class="toc level1 tocsp"><a href="gexaf.html">Preface</a></p>
<p class="toc level1 tocsp"><a href="gfirp.html">Part&nbsp;I&nbsp;Introduction</a></p>
<p class="toc level2"><a href="bnaaw.html">1.&nbsp;&nbsp;Overview</a></p>
<p class="toc level2"><a href="gfiud.html">2.&nbsp;&nbsp;Using the Tutorial Examples</a></p>
<p class="toc level1 tocsp"><a href="bnadp.html">Part&nbsp;II&nbsp;The Web Tier</a></p>
<p class="toc level2"><a href="bnadr.html">3.&nbsp;&nbsp;Getting Started with Web Applications</a></p>
<p class="toc level2"><a href="bnafd.html">4.&nbsp;&nbsp;Java Servlet Technology</a></p>
<p class="toc level2"><a href="bnagx.html">5.&nbsp;&nbsp;JavaServer Pages Technology</a></p>
<p class="toc level2"><a href="bnajo.html">6.&nbsp;&nbsp;JavaServer Pages Documents</a></p>
<p class="toc level2"><a href="bnakc.html">7.&nbsp;&nbsp;JavaServer Pages Standard Tag Library</a></p>
<p class="toc level2"><a href="bnalj.html">8.&nbsp;&nbsp;Custom Tags in JSP Pages</a></p>
<p class="toc level2"><a href="bnaon.html">9.&nbsp;&nbsp;Scripting in JSP Pages</a></p>
<p class="toc level2"><a href="bnaph.html">10.&nbsp;&nbsp;JavaServer Faces Technology</a></p>
<p class="toc level2"><a href="bnaqz.html">11.&nbsp;&nbsp;Using JavaServer Faces Technology in JSP Pages</a></p>
<p class="toc level2"><a href="bnatx.html">12.&nbsp;&nbsp;Developing with JavaServer Faces Technology</a></p>
<p class="toc level2"><a href="bnavg.html">13.&nbsp;&nbsp;Creating Custom UI Components</a></p>
<p class="toc level2"><a href="bnawo.html">14.&nbsp;&nbsp;Configuring JavaServer Faces Applications</a></p>
<p class="toc level2"><a href="bnaxu.html">15.&nbsp;&nbsp;Internationalizing and Localizing Web Applications</a></p>
<p class="toc level1 tocsp"><a href="bnayk.html">Part&nbsp;III&nbsp;Web Services</a></p>
<p class="toc level2"><a href="bnayl.html">16.&nbsp;&nbsp;Building Web Services with JAX-WS</a></p>
<p class="toc level2"><a href="bnazf.html">17.&nbsp;&nbsp;Binding between XML Schema and Java Classes</a></p>
<p class="toc level2"><a href="bnbdv.html">18.&nbsp;&nbsp;Streaming API for XML</a></p>
<p class="toc level2"><a href="bnbhf.html">19.&nbsp;&nbsp;SOAP with Attachments API for Java</a></p>
<p class="toc level1 tocsp"><a href="bnblr.html">Part&nbsp;IV&nbsp;Enterprise Beans</a></p>
<p class="toc level2"><a href="bnbls.html">20.&nbsp;&nbsp;Enterprise Beans</a></p>
<div class="onpage">
<p class="toc level3"><a href="">What Is an Enterprise Bean?</a></p>
<p class="toc level4"><a href="#bnblu">Benefits of Enterprise Beans</a></p>
<p class="toc level4"><a href="#bnblv">When to Use Enterprise Beans</a></p>
<p class="toc level4"><a href="#bnblw">Types of Enterprise Beans</a></p>
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<p class="toc level3 tocsp"><a href="bnbly.html">What Is a Session Bean?</a></p>
<p class="toc level4"><a href="bnbly.html#bnblz">State Management Modes</a></p>
<p class="toc level5"><a href="bnbly.html#bnbma">Stateful Session Beans</a></p>
<p class="toc level5"><a href="bnbly.html#bnbmb">Stateless Session Beans</a></p>
<p class="toc level4 tocsp"><a href="bnbly.html#bnbmc">When to Use Session Beans</a></p>
<p class="toc level3 tocsp"><a href="bnbmd.html">What Is a Message-Driven Bean?</a></p>
<p class="toc level4"><a href="bnbmd.html#bnbme">What Makes Message-Driven Beans Different from Session Beans?</a></p>
<p class="toc level4"><a href="bnbmd.html#bnbmf">When to Use Message-Driven Beans</a></p>
<p class="toc level3 tocsp"><a href="bnbmg.html">Defining Client Access with Interfaces</a></p>
<p class="toc level4"><a href="bnbmg.html#bnbmh">Remote Clients</a></p>
<p class="toc level4"><a href="bnbmg.html#bnbmj">Local Clients</a></p>
<p class="toc level4"><a href="bnbmg.html#bnbmk">Deciding on Remote or Local Access</a></p>
<p class="toc level4"><a href="bnbmg.html#bnbml">Web Service Clients</a></p>
<p class="toc level4"><a href="bnbmg.html#bnbmm">Method Parameters and Access</a></p>
<p class="toc level5"><a href="bnbmg.html#bnbmn">Isolation</a></p>
<p class="toc level5"><a href="bnbmg.html#bnbmo">Granularity of Accessed Data</a></p>
<p class="toc level3 tocsp"><a href="bnbmp.html">The Contents of an Enterprise Bean</a></p>
<p class="toc level3"><a href="bnbmr.html">Naming Conventions for Enterprise Beans</a></p>
<p class="toc level3"><a href="bnbmt.html">The Life Cycles of Enterprise Beans</a></p>
<p class="toc level4"><a href="bnbmt.html#bnbmu">The Life Cycle of a Stateful Session Bean</a></p>
<p class="toc level4"><a href="bnbmt.html#bnbmw">The Life Cycle of a Stateless Session Bean</a></p>
<p class="toc level4"><a href="bnbmt.html#bnbmy">The Life Cycle of a Message-Driven Bean</a></p>
<p class="toc level3 tocsp"><a href="bnbna.html">Further Information about Enterprise Beans</a></p>
<p class="toc level2 tocsp"><a href="bnbnb.html">21.&nbsp;&nbsp;Getting Started with Enterprise Beans</a></p>
<p class="toc level2"><a href="bnboc.html">22.&nbsp;&nbsp;Session Bean Examples</a></p>
<p class="toc level2"><a href="bnbpk.html">23.&nbsp;&nbsp;A Message-Driven Bean Example</a></p>
<p class="toc level1 tocsp"><a href="bnbpy.html">Part&nbsp;V&nbsp;Persistence</a></p>
<p class="toc level2"><a href="bnbpz.html">24.&nbsp;&nbsp;Introduction to the Java Persistence API</a></p>
<p class="toc level2"><a href="bnbrl.html">25.&nbsp;&nbsp;Persistence in the Web Tier</a></p>
<p class="toc level2"><a href="bnbrs.html">26.&nbsp;&nbsp;Persistence in the EJB Tier</a></p>
<p class="toc level2"><a href="bnbtg.html">27.&nbsp;&nbsp;The Java Persistence Query Language</a></p>
<p class="toc level1 tocsp"><a href="bnbwi.html">Part&nbsp;VI&nbsp;Services</a></p>
<p class="toc level2"><a href="bnbwj.html">28.&nbsp;&nbsp;Introduction to Security in the Java EE Platform</a></p>
<p class="toc level2"><a href="bnbyk.html">29.&nbsp;&nbsp;Securing Java EE Applications</a></p>
<p class="toc level2"><a href="bncas.html">30.&nbsp;&nbsp;Securing Web Applications</a></p>
<p class="toc level2"><a href="bncdq.html">31.&nbsp;&nbsp;The Java Message Service API</a></p>
<p class="toc level2"><a href="bncgv.html">32.&nbsp;&nbsp;Java EE Examples Using the JMS API</a></p>
<p class="toc level2"><a href="bncih.html">33.&nbsp;&nbsp;Transactions</a></p>
<p class="toc level2"><a href="bncjh.html">34.&nbsp;&nbsp;Resource Connections</a></p>
<p class="toc level2"><a href="bncjx.html">35.&nbsp;&nbsp;Connector Architecture</a></p>
<p class="toc level1 tocsp"><a href="bnckn.html">Part&nbsp;VII&nbsp;Case Studies</a></p>
<p class="toc level2"><a href="bncko.html">36.&nbsp;&nbsp;The Coffee Break Application</a></p>
<p class="toc level2"><a href="bnclz.html">37.&nbsp;&nbsp;The Duke's Bank Application</a></p>
<p class="toc level1 tocsp"><a href="gexbq.html">Part&nbsp;VIII&nbsp;Appendixes</a></p>
<p class="toc level2"><a href="bncno.html">A.&nbsp;&nbsp;Java Encoding Schemes</a></p>
<p class="toc level2"><a href="bncnq.html">B.&nbsp;&nbsp;Preparation for Java EE Certification Exams</a></p>
<p class="toc level2"><a href="bncnt.html">C.&nbsp;&nbsp;About the Authors</a></p>
<p class="toc level1 tocsp"><a href="idx-1.html">Index</a></p>
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<a name="bnblt"></a><h3>What Is an Enterprise Bean?</h3>
<p><a name="indexterm-2006"></a>Written in the Java programming language, an <b>enterprise bean</b> is a server-side component
that encapsulates the business logic of an application. The business logic is the
code that fulfills the purpose of the application. In an inventory control application,
for example, the enterprise beans might implement the business logic in methods called
<tt>checkInventoryLevel</tt> and <tt>orderProduct</tt>. By invoking these methods, clients can access the inventory services
provided by the application.</p>

<a name="bnblu"></a><h4>Benefits of Enterprise Beans</h4>
<p><a name="indexterm-2007"></a>For several reasons, enterprise beans simplify the development of large, distributed applications. First,
because the EJB container provides system-level services to enterprise beans, the bean developer
can concentrate on solving business problems. The EJB container, rather than the bean
developer, is responsible for system-level services such as transaction management and security authorization.</p><p><a name="indexterm-2008"></a><a name="indexterm-2009"></a>Second, because the beans rather than the clients contain the application&rsquo;s business logic, the
client developer can focus on the presentation of the client. The client developer
does not have to code the routines that implement business rules or access
databases. As a result, the clients are thinner, a benefit that is particularly
important for clients that run on small devices.</p><p>Third, because enterprise beans are portable components, the application assembler can build new
applications from existing beans. These applications can run on any compliant Java EE
server provided that they use the standard APIs.</p>

<a name="bnblv"></a><h4>When to Use Enterprise Beans</h4>
<p>You should consider using enterprise beans if your application has any of the
following requirements:</p>
<ul><li><p>The application must be scalable. To accommodate a growing number of users, you may need to distribute an application&rsquo;s components across multiple machines. Not only can the enterprise beans of an application run on different machines, but also their location will remain transparent to the clients.</p></li>
<li><p>Transactions must ensure data integrity. Enterprise beans support transactions, the mechanisms that manage the concurrent access of shared objects.</p></li>
<li><p>The application will have a variety of clients. With only a few lines of code, remote clients can easily locate enterprise beans. These clients can be thin, various, and numerous.</p></li></ul>


<a name="bnblw"></a><h4>Types of Enterprise Beans</h4>
<p><a name="indexterm-2010"></a><a href="#bnblx">Table&nbsp;20-1</a> summarizes the two types of enterprise beans. The following sections discuss each
type in more detail.</p><a name="bnblx"></a><h6>Table&nbsp;20-1 Enterprise Bean Types</h6><table><col width="29%"><col width="70%"><tr><th align="left" valign="top" scope="column"><p>Enterprise Bean Type</p></th>
<th align="left" valign="top" scope="column"><p>Purpose</p></th>
</tr>
<tr><td align="left" valign="top" scope="row"><p>Session</p></td>
<td align="left" valign="top" scope="row"><p><a name="indexterm-2011"></a><a name="indexterm-2012"></a>Performs a task for a client; optionally may implement
a web service</p></td>
</tr>
<tr><td align="left" valign="top" scope="row"><p>Message-Driven</p></td>
<td align="left" valign="top" scope="row"><p>Acts as a listener for a particular messaging type, such
as the Java</p><p>Message Service API</p></td>
</tr>
</table>
<hr><p><b>Note - </b>Entity beans have been replaced by Java Persistence API entities. For information about
entities, see <a href="bnbpz.html">Chapter&nbsp;24, Introduction to the Java Persistence API</a>.</p>
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